Other pressures of potential concern in the Celtic Sea ecoregion are the introduction of contaminating compounds: the introduction of non-indigenous species, litter, and underwater sound.

​​​​​​​​​​​Contaminants are localized and restricted to coastal
areas, with levels of most contaminants declining. However, polychlorinated biphenyls (PCBs) in both killer whales Orcinus orca
and bottlenose dolphins Tursiops truncatus are at levels that will inhibit reproduction.​